The present invention relates to a cylinder head, and more particularly relates to a cylinder head with a construction for a coolant plenum formed in it, which provides improved coolant flow and improved cylinder head cooling effect.
A typical cylinder head for an internal combustion engine is formed by casting, and has an inner wall, an outer wall and side walls, with a coolant plenum being defined between said inner wall and said outer wall. Coolant circulates through this coolant plenum from an inlet thereof to an outlet thereof, generally over the inner cylinder head wall which defines the roofs of the combustion chambers of the engine as well as past various structures such as walls enclosing spark plug holes for the spark plugs for the engine cylinders, bosses for slidably receiving intake and exhaust valves of the engine, bulges for defining intake and exhaust ports of the engine, and so on; and thereby this coolant flow cools these structures.
A problem that has arisen in this connection is that it is desirable to have such coolant flows over respective coolant paths defined in the coolant plenum that ensure a uniform temperature over various portions; but, due to the profusion of various structures such as those detailed above which restrict the cross sections of the coolant paths therearound, inevitably some other portions of said coolant paths come to be of undesirably greater cross sectional area. This means that the flow speed at these portions of the greater cross section is relatively lower than in other portions, and thereby not enough cooling action is available at these portions. This can cause hot spots to develop within the combustion chambers of the engine at locations corresponding to these coolant path portions, which can lead to problems with lubrication and deterioration of engine durability, as well as to knocking and loss of mechanical octane value of the engine or preignition of the fuel.
In the prior art, for example in Japanese Patent Application Ser. No. 55-52286 (1980) which was published as Japanese Patent Laying Open Publication Ser. No. 56-148647, there have been proposed to form projections which stick out into and obstruct those portions of the coolant paths where said coolant paths would otherwise be of undesirably large cross sectional area. Thereby, the above mentioned problems can in principle be resolved, but such projections have been in the prior art relatively hard to manufacture. The coolant plenum is typically formed by the use of a casting sand inner core during the casting process of the cylinder head, and, whether the projections are cast integrally with the cylinder head or are cast as inclusions into said cylinder head (which entails an undesirable increase in the number of parts for manufacturing the cylinder head), it is difficult to manufacture them economically. Accordingly, mass production of such a cylinder head at a reasonable cost level has been impracticable.